Process and apparatus for the treatment of waste water

ABSTRACT

A process and apparatus for treating waste water using a sequencing batch reactor system in conjunction with a membrane filtration device for solids/liquid separation provides a highly efficient method and apparatus for the removal of organic contaminants, nutrients and suspended solids from waste water. A three-phase cycle is used, consisting of a mix fill phase, a react fill phase and a react discharge phase. In the mix fill phase the reactor environment is controlled to provide an initial anaerobic time period for achieving phosphorous release and denitrification of oxidized nitrogen present in the reactor from the prior cycle. In the react fill phase waste water continues to enter the reactor. The reactor environment is controlled to provide alternating periods of aeration and mixing and mixing only to promote completely mixed aerobic and anoxic conditions. The alternating periods of aerobic and anoxic conditions promote the oxidation of organic and nitrogenous waste products and the biological uptake of phosphorous followed by the denitrification of oxidized nitrogen. Finally, in the react discharge phase, waste water flow into the reactor ceases. The reactor environment is still controlled to provide alternating periods of aerobic and anoxic conditions. The waste water in the reactor is directed to a membrane device for solids/liquid separation. The solids/liquid mixture that does not pass through the membrane is returned to the reactor. This treatment approach eliminates the necessity to provide separate anaerobic and anoxic basins. The combination of the membrane device with the sequencing batch reactor process eliminates the necessity to provide appropriate time periods for a quiescent environment for solids/liquid separation and the requirement of mechanical decanter devices normally required to extract the desired effluent quality in conventional sequencing batch reactor systems.

FIELD OF THE INVENTION

[0001] The present invention relates generally to processes andapparatus for the treatment of waste water and, more particularly, toprocesses and apparatus for efficiently removing organic contaminants,nutrients and suspended solids from waste water using a sequencing batchreactor system in conjunction with a membrane filter device.

BACKGROUND OF THE INVENTION

[0002] The claimed invention involves the use of microorganisms,forexample, bacteria in activated sludge, to metabolize organiccontaminants in waste water while simultaneously removing nutrients suchas nitrogen and phosphates, in conjunction with a membrane to effect theremoval of suspended solids from waste water.

[0003] Organic compounds in waste water typically have a highbiochemical oxygen demand (BOD). Under aerobic conditions, bacteria inactivated sludge metabolize this BOD in three ways:(1) substrateoxidation in which organic compounds are converted to carbon dioxide andwater; (2) synthesis in which organic compounds and nutrients areconverted to cell protoplasm; and (3) endogenous respiration in whichprotoplasm is converted to carbon dioxide, nutrients and water.

[0004] Nitrogen is typically present in waste water in the forms oforganic nitrogen and ammonia (NH₄ ⁻). The process of removing thiscontaminant requires two distinct steps in which organic nitrogen ishydrolyzed and ammonia is converted to free nitrogen gas (N₂) which canreadily be stripped from solution to the atmosphere. First, in thenitrification process, ammonia is converted to nitrate (NO₂ ⁻) byautotrophic oxidation involving Nitrosomonas spp. and related organisms,followed by further oxidation to nitrate (NO₃ ⁻) involving Nitrobacterspp. Second, in the denitrification process, a relatively broad range ofheterotrophic facultative organisms convert nitrate to free nitrogen(N₂) in a series of steps.

[0005] It is apparent that the nitrogen removal process, as describedabove, requires first an aerobic step in which the oxidation of ammoniato nitrate takes place (nitrification), followed by an anoxic step inwhich facultative organisms convert nitrate and nitrite to free nitrogenwhich can be released (denitrification),

[0006] The removal of phosphates takes place in two steps and ismediated by a group of phosphorous rich microorganisms (Bio-P),principally Acinetobacter spp. and some Aeromonas. These organisms, whenpresent in sludge exposed to anaerobic condition, use stored energy inthe form of poly-phosphate to absorb food materials, for example,volatile fatty acids such as acetic, propionic, or butyric acids formedin the activated sludge as a result of exposure to anaerobic conditions)and store it as poly-B-hydroxybutyrate (PHB). In the process, theorganisms release phosphates as the polyphosphates are broken down torelease energy. The conditions must be anaerobic rather than anoxic toallow for the depletion of nitrates which would inhibit phosphaterelease and the absorption of volatile fatty acids by themicroorganisms.

[0007] In the second step of phosphate removal, under aerobicconditions, the aerobic bacteria contained in the activated sludgemetabolize the PHB and take up phosphates as biomass increases. Morephosphate is taken up by the Bio-P organisms than was previouslyreleased, a difference known as luxury uptake.

[0008] In addition to the organic and inorganic contaminants describedabove, waste water typically contains suspended solids in the forms ofmicroorganisms and endogenous mass in the activated sludge and inertorganic and inorganic mass in the waste water itself, which must beremoved before the liquid is returned to the environment. These solidsare typically 0.5 microns or greater in size. In conventional wastewater treatment systems the solids are removed from the liquid throughgravitational sedimentation and decanting. A quiescent environment isprovided for a sufficient amount of time for the solids to separate fromthe liquid, and then a mechanical decanter withdraws the purified water.

[0009] Waste water treatment processes and apparatus have been developedto provide the above-described conditions necessary for the removal oforganic contaminants, nitrogen, phosphates and suspended solids. Forexample, so-called “linear” waste water treatment processes have beendeveloped which comprise a series of tanks or basins in which wastewater is sequentially subjected to anaerobic and aerobic conditions, andis then pumped to a clarifier where suspended solids are separated fromthe purified liquid and the liquid is decanted.

[0010] Although this system combines anaerobic, aerobic and clarifyingprocesses, thereby allowing for the removal of organic contaminants,inorganic nutrients and suspended solids, the system is relativelyinefficient as it requires numerous tanks, large volumes of liquid andlong retention times.

[0011] Conventional sequencing batch reactor (SBR) processes have beendeveloped to address these inefficiencies. In an SBR process, wastewater is mixed with activated sludge, exposed to intermittent aerobicand anoxic/anaerobic conditions and further purified through settlingand decanting in a single vessel. This is typically accomplished througha series of cycles including fill, react, settle and decant phases.

[0012] In the fill phase, waste water enters the reactor where it ismixed with activated sludge therein. Aeration is typically intermittentto promote aerobic or anoxic/anaerobic conditions. In the react phase,influent flow is terminated while mixing and aeration continue. Again,aeration is typically intermittent to allow for the removal of nitrogenand phosphorous. In the settle phase, mixing and aeration cease andsolids/liquid separation takes place under quiescent conditions. In thedecant phase of the cycle, the mixer and aeration systems remain off andthe decantable liquid volume is removed by means of a subsurfacewithdrawal. A typical SBR process cycle requires four to eight hours tocomplete.

[0013] Two reactors may be used in parallel to permit a continuous flowto the system. The total time required for the mixed fill and react fillphases in the first reactor is equal to the time required for the react,settle and decant phases in the second reactor. In this process, 100% ofthe flow is directed to each reactor 50% of the time. For example, flowtypically enters the system for 24 hours of each day. Each reactor wouldreceive flow for a 12-hour period. In a given 12-hour period, the firstreactor may be receiving waste water, in the mixed fill and react fillphases, while the second reactor is not receiving flow, as it is in thereact, settle or decant phases. At the end of the 12-hour period, thesecond reactor has completed its treatment cycle and is ready to receiveflow for 12 hours. The first reactor begins the react, settle and decantphases.

[0014] While conventional SBR processes as described above offersignificant advantages over linear and other known waste water treatmentprocesses, such as more efficient settling, decreased operational costsand higher treatment efficiencies, conventional SBR processesnevertheless have shortcomings. For example, the settle phase of eachcycle requires quiescent conditions for an appropriate period of time toallow solids/liquid separation, which can require several hours. And insome applications, particularly where the amount of solids is large orthe settling characteristics of the solids are imperfect, the settlingprocess does not adequately separate solids from the liquid.Furthermore, the decant phase of each cycle typically requires the useof an expensive mechanical device to extract the desired effluentquality.

[0015] The present invention eliminates the need for a mechanicaldecanter device and the necessity of settle and decant phases, whilestill accomplishing the removal of organic matter, nitrogen, phosphorousand suspended solids to achieve effluent quality achieved inconventional SBR systems. Specifically, the invention uses a membranefiltration device in conjunction with an SBR process to accomplishsolids/liquid separation while at the same time providing alternating,mixed aerobic and anoxic/anaerobic conditions which optimize effluentquality. Since the settle and decant phases of the cycle are eliminated,greater volumes of waste water can be treated in less time as comparedwith conventional SBR systems. An entire treatment cycle can becompleted in approximately two hours. The membrane also increases theefficiency of solids/liquid separation. Adequate separation is achievedeven with large amounts of suspended solids that have imperfect settlingcharacteristics. Moreover, because a mechanical decanting device is notneeded, construction, operation and maintenance costs are less thanthose associated with conventional SBR systems.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The invention will be better understood by reference to thedrawings.

[0017]FIG. 1A is a flow chart showing the steps used in the watertreatment method in accordance with the present invention.

[0018]FIG. 1B is a flow chart showing the steps typically required in aconventional SBR process.

[0019]FIG. 2 is a schematic flow diagram of a water treatment system inaccordance with the present invention.

[0020]FIG. 3 is diagrammatic view of a membrane in accordance with thepresent invention showing the flow of liquid/solids therethrough.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

[0021] Set forth below is a description of what is currently believed tobe a preferred embodiment or best example of the invention claimed.Future and present alternatives and modifications to this embodiment arecontemplated. Any alternatives or modifications which make insubstantialchanges in function, purpose, structure or result are intended to becovered by the claims of this patent.

[0022] An overview of the operation of the process and apparatus of thepresent invention is illustrated in the form of the flowchart at FIG.1A. In step 100, waste water is drawn into a reactor containing anactivated sludge. A three-phase treatment cycle begins with step 105,the “mix fill phase.” In this phase, the waste water is thoroughly mixedwith the sludge. The reactor is not aerated, thereby creating ananoxic/anaerobic environment in which phosphorous release occurs.

[0023] In the “react fill” phase of operation, step 110, waste waterflow continues into the reactor. Mixing of the waste water and sludgecontinues. The waste water that has already entered and continues toenter the reactor represents a BOD which is sorbed, assimilated andmetabolized by the sludge. To allow for the removal of nitrogen andphosphorous, aeration in the reactor is intermittent, creatingalternating aerobic and anoxic environments.

[0024] Finally, in the “react discharge phase,” step 115, waste waterflow into the reactor ceases. The reactor continues to be intermittentlyaerated to create alternating aerobic and anoxic environments. The wastewater is directed to a membrane device for separation of solids from theliquid.

[0025] Some of the advantages of the processes and apparatus of thepresent invention are apparent by comparing them to a conventional SBRprocess, as depicted in FIG. 1B.

[0026] Like the present invention, a typical SBR process begins with thedrawing of waste water into a reactor 120, followed by a mix fill phase125 and a react fill phase 130. However, a typical SER process thenrequires a separate “react phase” 135 in which mixing of the waste waterand activated sludge continues and aeration is provided intermittentlyto further facilitate the removal of organic matter and nitrogen.

[0027] The react phase is followed by a “settle phase” 140 during whichthere is no waste water flow, mixing or aeration, thereby resulting in aquiescent environment for solids/liquid separation through gravitationalsedimentation.

[0028] Next, a “decant phase” 145 is required in which, typically, in aquiescent environment, a mechanical decanter is used to remove purifiedliquid from the reactor. Finally, an “idle phase” 150 may be required tosynchronize operation with a companion reactor.

[0029] The settle and decant phases are not required in the processesand apparatus of the present invention, which collapses the five-phasecycle into a three-phase cycle while providing all the benefits ofconventional SBR systems in addition to the significant benefitsexplained herein.

[0030]FIG. 2 depicts a waste treatment system 200 that applies theprinciples of the present invention. The system 200 may be comprised ofbioreactors 210 and 215 containing activated sludge, a membranefiltration unit 220 and accessory equipment described in detail below.While two bioreactors are used in the present embodiment, a greaternumber of bioreactors, or a single bioreactor, could be used inaccordance with the invention. The bioreactors 210 and 215 may operatein a two-hour treatment cycle that is comprised of three phases ofoperation. The first phase, mix fill, may last approximately 15 minutes.The second phase, react fill, may last approximately 45 minutes. Thefinal phase, react discharge, may last approximately 60 minutes. Wheretwo bioreactors are used, as the first bioreactor 210 completes the mixfill and react fill phases, the second bioreactor 215 will complete thereact discharge phase.

[0031] Influent may be drawn into either bioreactor 210 or 215bioreactor as determined by the position of influent valves 225 and 230.The influent may be drawn into the bioreactors by the force of gravityor, if necessary, influent pumps 235 and 240.

[0032] Influent valve 225 opens during the mix fill and react fillphases for the first bioreactor 210 and closes during the reactdischarge phase. In a similar manner influent valve 230 controls theflow to the second bioreactor 215. During operation of the system 200,the influent valves 225 and 230 will either open or close to control theflow to the bioreactors 210 and 215.

[0033] Level sensors 245 and 250 may be located in bioreactors 210 and215, respectively, to terminate flow into the bioreactors when waterreaches a desired level. The first bioreactor 210 is equipped withmixers 254 and 255, and the second bioreactor 215 is equipped withmixers 260 and 265. Although the present embodiment uses two mixers ineach bioreactor, any number of mixers may be used to achieve sufficientmixing of the waste water and activated sludge. In the presentembodiment, the mixers operate continuously during all phases of thetreatment cycle.

[0034] The first bioreactor 210 is equipped with an aerating means suchas a blower 270, corresponding blower valve 275 and a rotameter 280.Similarly, the second bioreactor 215 is equipped with an aerating meanssuch as blower 285, corresponding blower valve 290 and rotameter 295.Multiple or other aerating means, valves and rotameters may be used. Inthe present embodiment, each blower and corresponding blower valve isequipped with five sets of “On/Off” adjustable timer values that extendfrom the start of the react fill phase to the end of the react dischargephase to permit the creation of either aerobic or anoxic conditions ineach bioreactor, as required.

[0035] The membrane filtration subsystem 300 withdraws flow from thefirst or second bioreactor 210 or 215 during the react discharge phaseof the cycle for each bioreactor. The subsystem includes a membranefiltration unit 220 and discharge valves 310 and 315, which control theflow of liquid/solids from bioreactor 210 or 215 to the suction port ofthe membrane pump 320. Return flow valves, 325 and 330, are equippedwith operators and control the return flow of liquid/solids from themembrane filtration subsystem 300 to either bioreactor 210 or 215.Membrane pump 320 operates continuously and the opening or closing ofthe appropriate discharge valve and return flow valve combination willpermit the withdrawal and return of liquid/solids to either bioreactor.In general, discharge valve 310 and return flow valve 325 operate aseither an open or closed combination and discharge valve 315 and returnflow valve 330 operate in a similar manner.

[0036] Level sensor 335, located in bioreactor 210, and level sensor340, located in bioreactor 215 may be used to terminate the flow ofliquid/solids upon attaining a specified low water level by closing thedischarge valve 310 or 315 and the return flow valve 325 or 330 andstopping the membrane pump 320.

[0037] The following Table I identifies the status of each of thesesystem components during a typical two-hour treatment cycle of thepresent embodiment. TABLE I ITEM 0-15 min. 15-60 min. 60-75 min. 75-120min. Influent ON ON ON ON Pump 235 Influent ON ON ON ON Pump 240Influent OPEN OPEN CLOSED CLOSED Valve 225 Influent CLOSED CLOSED OPENOPEN Valve 230 Mixer 254 ON ON ON ON Mixer 255 ON ON ON ON Mixer 260 ONON ON ON Mixer 265 ON ON ON ON Level Sensor CLOSED CLOSED CLOSED CLOSEDHigh Water 245 Level Sensor CLOSED CLOSED CLOSED CLOSED Low Water 335Level Sensor CLOSED CLOSED CLOSED CLOSED High Water 250 Level SensorCLOSED CLOSED CLOSED CLOSED Low Water 340 Blower 270 OFF ON ON ON Blower285 ON ON OFF ON Blower CLOSED OPEN OPEN OPEN Valve 275 Blower OPEN OPENCLOSED OPEN Valve 290 Discharge CLOSED CLOSED OPEN OPEN Valve 310Discharge OPEN OPEN CLOSED CLOSED Valve 315 Return Flow CLOSED CLOSEDOPEN OPEN Valve 325 Return Flow OPEN OPEN CLOSED CLOSED Valve 330Membrane ON ON ON ON Pump 320

[0038] The membrane filtration unit 220 is explained in more detail withreference to FIG. 3. The unit includes membrane 400, including pores405. Although the present embodiment uses a single membrane, any numberof membranes may be required to achieve sufficient effluent quality. Thesize of the pores are small enough to prevent waste water solids frompassing through the membrane, but large enough to minimize the pressurerequired to force water through the membrane. In a typical applicationan ultrafiltration type membrane with a pore size ranging from 0.001 to0.02 micron or a microfiltration type membrane with a pore size rangingfrom 0.1 micron to 5.0 microns is suitable, with an operating pressurein the membrane filtration subsystem 300 of about 60 psi. As will beappreciated by those skilled in the art, various pore sizes andpressures can be used, depending on the particular application.

[0039] Various membrane configurations may be used in the presentinvention so long as the membrane provides an adequate surface area forwater processing and acceptable permeation and recovery rates, but doesnot clog or foul easily. Furthermore, the membrane must be made of amaterial that is tolerant to a wide range of temperature, and ischemically inert and resistant to constant pressurized operations.Membranes meeting these requirements are well known to persons ofordinary skill in the art.

[0040] A microfiltration capillary membrane of the type manufactured byPall Corporation, 2200 Northern Boulevard, East Hills, N.Y. 11548 isbelieved to be particularly suitable for use in the present invention.The membrane is comprised of capillary membrane tubes in a housing. Theaverage diameter of each membrane tube is about 1 to 2 mm. The directionof waste water flow is parallel to the membrane wall. Water permeatesthrough the membrane 400 while the solids are continuously carried awayfrom the membrane surface, thus minimizing clogging of the pores 405.

[0041] The above description is not intended to limit the meaning of thewords used in the following claims that define the invention. Rather, itis contemplated that future modifications in function, purpose,structure or result will exist that are not substantial changes and thatall such insubstantial changes in what is claimed are intended to becovered by the claims.

What is claimed is:
 1. A process for the treatment of waste water,comprising the steps of: drawing waste water into a vessel containing anactivated sludge; mixing the waste water and the activated sludge in thevessel to create a mixture; exposing the mixture in the vessel toanaerobic conditions for a sufficient time to permit the release ofphosphorous and denitrification of oxidized nitrogen; exposing themixture in the vessel to alternating periods of aerobic and anoxicconditions for a sufficient time to permit the oxidation of organiccontaminants in the waste water and nitrogenous waste products and theuptake of phosphorous followed by the denitrification of oxidizednitrogen; extracting the mixture from the reactor while exposing themixture to alternating periods of aerobic and anoxic conditions; andpassing the mixture through a membrane unit to separate suspended solidsin the mixture from liquid.
 2. The process of claim 1 wherein said stepsof mixing the waste water and the activated sludge in the vessel tocreate a mixture and exposing the mixture in the vessel to anaerobicconditions for a sufficient time to permit the release of phosphorousand denitrification of oxidized nitrogen are completed in about 15minutes.
 3. The process of claim 1 wherein the step of exposing themixture in the vessel to alternating periods of aerobic and anoxicconditions for a sufficient time to permit the oxidation of organiccontaminants in the waste water and nitrogenous waste products and theuptake of phosphorous followed by the denitrification of oxidizednitrogen is completed in about 45 minutes.
 4. The process of claim 1wherein the steps of extracting the mixture from the reactor whileexposing the mixture to alternating periods of aerobic and anoxicconditions and passing the mixture through a membrane unit to separatesuspended solids in the mixture from liquid are completed in about 60minutes.
 5. A device for the treatment of waste water, comprising: abioreactor containing an activated sludge therein; a filtration unitincluding a membrane; one or more valves for controlling the flow intothe bioreactor; one or more pumps for controllably pumping waste waterinto the bioreactor; one or more mixers for mixing the waste water withthe activated sludge in the bioreactor to create a mixture; one or moreblowers for controllably aerating the waste water and activated sludgein the bioreactor at designated intervals; one or more valves forcontrolling the flow of the mixture from the bioreactor to thefiltration unit; a pump for pumping the mixture through the membrane ofthe filtration unit such that solids in the mixture are separated fromliquid in the mixture; and, one or more valves for controlling thereturn flow of the mixture from the filtration unit to the bioreactor.6. A device for the treatment of waste water, comprising: a firstbioreactor containing an activated sludge therein; a second bioreactorcontaining an activated sludge therein; a filtration unit including amembrane; one or more valves for controlling the flow into the first andsecond bioreactors at designated intervals; one or more pumps forcontrollably pumping waste water into the first and second bioreactorsat designated intervals; one or more mixers for mixing the waste waterwith the activated sludge in the first and second bioreactors to createa mixture in each bioreactor; one or more blowers for controllablyaerating the waste water and activated sludge in the first and secondbioreactors at designated intervals; one or more valves for controllingthe flow of the mixture from each of the first and second bioreactors tothe filtration unit; one or more pumps for pumping the mixture throughthe membrane of the filtration unit such that solids in the mixture areseparated from liquid in the mixture; one or more valves for controllingthe return flow of the mixture from the filtration unit to eachbioreactor; wherein, as the first bioreactor performs mix fill and reactfill phases of operation, the second bioreactor performs a reactdischarge phase of operation and as the first bioreactor performs thereact discharge phase of operation, the second bioreactor performs themix fill and react fill phases of operation.